The present invention relates to oil well production and, more particularly, to a method and apparatus for downhole stimulation of oil production from a well.
Current techniques for cleaning or stimulating an oil well include the injection of various well known solvents and acids into the production zone of a well. The solvents or acids cause the asphaltenes in the zone to break up and flow through the perforations in the slotted well casing. The solvents or acids also dissolve or dilute contaminants such as scale, bitumen, sediment and the like which may be plugging the casing slots thereby allowing oil in the production zone to more readily flow into the casing and eventually be brought to the surface.
Recently a cleaning technique has been employed which utilized a cleaning device generating a high pressure gas pulse downhole in the region of the casing slots. A flexible tubing encasing a gas generating propellant is run into the perforated section of the casing on a single conductor cable. The propellant is ignited by means of an ignition mechanism thereby producing a gas to propel, high velocity, short duration flow of well fluid and gas through the perforations. This is followed by cooling and contraction of the gas which creates an implosion and flow of fluids into the well bore from the annulus, gravel pock or formation. Thus a double acting outflow-inflow is used to clean the perforations and create flow channels in the annulus. It must be understood that a series of pulses may not be created as the device is withdrawn from the production zone, since there is only a single length of propellant which is ignited.
It is well known in the seismic exploration for hydrocarbons and minerals, oceanographic research, deep earth crustal studies, and well velocity surveys that powerful energy sources may be utilized to create waveforms for mapping purposes. One of these sources is known by the trademark BOLT
AIR GUN. Such guns are available in over twenty variations of seven basic models for use at sea and on land, both downhole and on the surface. The guns operate by the principle of the sudden release of high pressure compressed gas, such as air or nitrogen, when electrically fired. A high degree of repeatability may be obtained, allowing the use of multi-gun arrays to achieve high energy output and optimally synthesized waveforms. Such guns have not been used to stimulate producing wells or to clean casing perforations by combining the acoustic pressure pulse with simultaneous injection of solvents or acids into the production zone.